Convert CONFIG_BOARD_EARLY_INIT_F to Kconfig

This converts the following to Kconfig:
   CONFIG_BOARD_EARLY_INIT_F

Signed-off-by: Simon Glass <sjg@chromium.org>
diff --git a/configs/mx6qarm2_lpddr2_defconfig b/configs/mx6qarm2_lpddr2_defconfig
index a3694b0..0f80ba1 100644
--- a/configs/mx6qarm2_lpddr2_defconfig
+++ b/configs/mx6qarm2_lpddr2_defconfig
@@ -3,6 +3,7 @@
 CONFIG_TARGET_MX6QARM2=y
 CONFIG_SYS_EXTRA_OPTIONS="IMX_CONFIG=board/freescale/mx6qarm2/imximage.cfg,MX6Q,MX6DQ_LPDDR2,DDR_MB=512"
 CONFIG_BOOTDELAY=3
+CONFIG_BOARD_EARLY_INIT_F=y
 CONFIG_HUSH_PARSER=y
 CONFIG_CMD_BOOTZ=y
 # CONFIG_CMD_IMLS is not set